FAQ.md

FAQ

• How GMock works?

  • It's not a C++ standard solution (depends on vtable implementation)

    • Itanium C++ ABI (vtable)
    • VTable in GCC
    • Deleting Destructors
    • Devirtualization in C++
    • Member Function Pointers and the Fastest Possible C++ Delegates
    • Reversing C++ Virtual Functions
    • C++ vtables
    • g++ -fdump-class-hierarchy interface.hpp

  • Similar projects (FakeIt, HippoMocks)

• How quick is GMock?

  • Compile time benchmark (Example)

    Compiler	Number of Mocks	GoogleMock/GoogleTest	GoogleMock/GoogleTest + GUnit
    GCC-6	3	2.6s	2.1s
    Clang-3.9	3	2.3s	1.9s

• But virtual function call has performance overhead?

  • This statement is not really true anymore with modern compilers as most virtual calls might be inlined
    • Devirtualization in C++
    • Using final - C++11
    • Link Time Optimization - LTO

• Limitations

  • GMock can't mock classes with multiple or virtual inheritance
  • GMock, by default, can fake interface with up to 128 virtual methods

• Integration tests with Dependency Injection ([Boost].DI)

class example; // System Under Test

GTEST(example) {
  namespace di = boost::di;

  SHOULD("create example") {
    const auto injector = di::make_injector(
      di::bind<interface>.to(di::NiceGMock{mocks})
    , di::bind<interface2>.to(di::StrictGMock{mocks})
    );

    sut = testing::make<SUT>(injector);

    EXPECT_CALL(mock<interface>(), (get)(_)).WillOnce(Return(123));
    EXPECT_CALL(mock<interface2>(), (f2)(123));

    sut->update();
  }
}